A lorry driver is in a serious condition in hospital after his vehicle collided with another lorry on the M4 in Berkshire.
The accident, on the westbound carriageway between Chieveley and Hungerford, has caused major delays.
The Highways Agency says it is likely to take until this afternoon for traffic to get back to normal.
Thames Valley Police are appealing for witnesses to the collision, which happened at 2.38am.
No arrests have been made at this stage.
Investigating Officer, Sgt Tony Griffiths of the Joint Operations Roads Policing Unit, said: “We are appealing for anyone who was travelling on the M4 in either direction this morning between the times of 2.30am and 3am near to Junction 13 and 14 of the M4 Westbound to come forward as they may have information to help us with our investigation.
Three fire engines attended along with a heavy rescue unit.
The westbound carriageway remains closed, with severe traffic congestion on both the M4 and A34.
Diversions are in place.
A34 N/B at #Hinksey hill closed due to serious RTC. Number of vehicles involved. Traffic diversion at Abingdon South. Investigation ongoing.
The A34 northbound carriageway has reopened after a crash involving four cars and four lorries.
Emergency services were called to the road near East Ilsley just after 5pm yesterday afternoon.
Four people were killed in the collision and twelve people were injured. Several people were treated at the scene for minor injuries.
A man has been arrested on suspicion of causing death by dangerous driving.
The A34 southbound is blocked before Whitchurch due to an overturned lorry. The incident happened just north of Whitchurch on the southbound carriageway.
The main northbound carriageway is closed due to overrunning overnight roadworks on the A34 Northbound at A4130 (Milton Interchange).
The two main lanes of the A34 remain closed because overnight works have not finished yet. A diversion is in place via the slip road.
The A34 southbound is blocked due to accident before M4 J13 ( Chieveley / Newbury). All traffic is being held just before the M4.
Police are appealing for witnesses to a crash on the A34 yesterday evening, in which a man died.
It happened at around 5.45pm on the northbound carriageway near the Tufton crossroads.
A Vauxhall Zafira collided with an HGV lorry which had initially been travelling in the same direction.
The front seat passenger of the Vauxhall Zafira, a 53-year-old man from Swindon in Wiltshire, was pronounced dead at the scene. The driver, a 40-year-old man, and two rear seat passengers (a 13-year-old girl and 38-year-old man) sustained minor injuries.
The driver of the HGV, a 48-year-old man from Poland, has been arrested on suspicion of causing death by dangerous driving and remains in custody.
I would appeal to anyone who was travelling northbound or southbound yesterday evening who may have witnessed the incident, or saw either vehicle before the collision to contact us as soon as possible.
There are major delays on the A34 tonight. The Northbound carriage is blocked after a lorry jackknifed between the M4 at Chieveley and East Ilsley junction. Fire crews are working to contain a fuel spillage. The road is likely to remain shut for the rest of the evening
A 50 mph speed limit is being introduced today along part of the A34 in Oxfordshire as drainage works take place.
The Highways Agency says the six month project between the junctions at Chilton and the Milton Interchange should help reduce flooding, and improve safety.
There will also be overnight lane closures and carriageway closures.
The improvements will mean new filter drains and pipes, which should result in less unplanned road closures due to emergency road maintenance.
This work will provide smoother and safer journeys for users of the A34 in this part of Oxfordshire. Road users will benefit from a section more resistant to flooding and therefore less likely to impact upon journeys. While work of this nature inevitably causes some inconvenience, we will aim to prevent as much disruption as possible."
Seventeen firefighters and a rescue support vehicle were called to a road traffic collision on the A34 northbound by Whitchurch this morning.
Despite initial reports, no-one was found to be trapped. Fire crews dealt with two people - providing them with first aid, and cleared up the scene of the collision which involved a taxi.